1. Field of the Invention
The present invention relates to a belt unit used for an image forming apparatus such as a copy machine, a printer, or a facsimile and an image forming apparatus including the belt unit.
2. Description of the Related Art
In general, endless belts such as intermediate transfer belts or secondary transfer belts are used for image forming apparatuses forming images according to an electrophotographic system. As such endless belts, for example, there are known belts built into intermediate transfer belt units so that the belts are extended by extension members such as a plurality of support rollers and cleaning counter rollers and cleaning blades come into contact with the outer peripheral surfaces thereof.
For example, as disclosed in JP-A-2006-151697, an intermediate transfer belt unit includes a pressure roller pressurizing an intermediate transfer belt from the outer peripheral side, and a tension force on the intermediate transfer belt is released by lifting up the entire belt unit at the time of belt exchange, so that the intermediate transfer belt is extracted from the extension members to be exchanged.
As disclosed in JP-A-2003-167402, an intermediate transfer belt is configured to be built in a support frame and a belt unit is designed to be downsized by setting the support frame as a plurality of unit bodies separable in a direction intersecting a direction of conveyance of the intermediate transfer belt and providing a bending point on a valley side to be bent in a direction in which the entire outer periphery of the support frame is smaller than the inner periphery of an endless belt.
However, for example, when an endless belt with a small diameter is extended by a plurality of extension rollers, it is difficult to slacken the belt so that the intermediate transfer belt is exchanged even when the tension force on the intermediate transfer belt is released by lifting up the entire belt unit or the belt support frame including the extension rollers is separated and bent, as described above. For this reason, it is necessary to separate the extension rollers from support members, and thus there is a problem in that it takes considerable time to exchange the intermediate transfer belt.
This problem is not limited only to the intermediate transfer belt, but also is common to a secondary transfer belt configured to transfer a toner image to a recording medium passed to be conveyed between an image carrier of an intermediate transfer belt or the like and the secondary transfer belt when the recording medium comes into contact with the image carrier. Therefore, the foregoing problem may be more conspicuous in such a secondary transfer belt with a small diameter.